Abstract: To improve the ride comfort of construction machineries, a 6-degree-of-freedom model of cab isolation system was established where rubber mounts were modeled as three-dimensional isolators and an optimal design approach to taking into account the control of cab shaking in low frequency range was proposed in this article. The vibration total value of weighted r.m.s acceleration response in the cab mass center, defined as the optimization objective, was calculated under the excitations at principal frequencies in 1/3 octaves from the frequency range 1 to 80 Hz where the human body was sensitive. And the optimization model which defined stiffness values as design variables was developed. Finally, a finite element model of a loader cab isolation system was built for the optimization design example, and the results showed that the vertical response at the center of the seat decreased significantly and the coupling between bouncing and pitching modes became weak. The test results showed that the isolation properties of the cab in three directions were all improved and the proposed optimization model was reasonable.